Vitest Workspace Errors - "Cannot define workspace" in a Monorepo

Vitest workspaces let one command run every package’s tests, but the configuration is easy to get wrong: a workspace defined in two places, a glob that matches nothing, or a per-package config that conflicts with the root.

What this error means

Running Vitest at the monorepo root errors about the workspace - no projects matched the workspace glob, or it complains that workspace and inline projects are both defined. Individual packages test fine in isolation.

Vitest output

Error: Vitest workspace was not able to resolve any projects.

  workspace: ['packages/*']
  matched: 0 projects

Make sure each project has a vitest/vite config or a "test" field.

Common causes

Workspace glob matches no valid projects

The vitest.workspace.ts glob points at directories that have no Vitest/Vite config or test field, so Vitest resolves zero projects and exits.

Workspace defined in conflicting places

Defining both a vitest.workspace.ts file and an inline test.projects in the root config (or two workspace files) makes Vitest ambiguous about which to use.

How to fix it

Define one workspace that matches real projects

vitest.workspace.ts

// vitest.workspace.ts
export default [
  'packages/*',          // each must have a vite/vitest config
  { test: { name: 'unit', root: './app' } },
];

Verify each project resolves

Confirm every globbed directory has a vite.config/vitest.config or a test field.
Remove duplicate workspace definitions - keep a single source of truth.
Run vitest --project <name> to validate one project at a time.

How to prevent it

Keep exactly one workspace definition for the monorepo.
Ensure every globbed package ships its own Vitest/Vite config.
Test the workspace resolution in CI so an empty match is caught.